1. Field of the Invention
The present invention relates to an alternator for use in an automotive vehicle, and more particularly to an alternator having cooling air intake windows each having an uneven opening area along a rotational direction of a cooling fan.
2. Description of Related Art
An amount of noises generated by a cooling fan of an alternator varies in accordance with a fan shape, a shape of cooling air intake windows and a form of a fan shroud. As to the fan shape, various proposals have been made to suppress the fan noises. In those proposals, the number of fan blades and the fan shape are variously changed to reduce noises generated by the cooling fan. As to the shape of the cooling air intake windows, JP-A-7-107704 proposes to form the windows in a non-circular shape and to shape the windows in various shapes different from one another in order to disperse order components of fan noises and thereby to suppress the noises as a whole.
As to the form of the fan shroud, French Patent Publication No. 2745439 proposes to make spokes of a housing in a slanted relation relative to a radial direction. A shroud surface facing fan blades is formed on a rear surface of each spoke, and pressure changes occurring when the fan blades pass each shroud surface are smoothened by slanting the spokes. In this manner, the fan noises are suppressed.
The proposal made by the above-mentioned JP-A-7-107704, however, changes only the shape of the cooling air intake windows and does not consider a pressure deviation in a space between fan blades and a fan shroud. Although the above-mentioned French Patent Publication proposes to form the spokes in a slanted relation relative to the radial direction, it is not desirable to form the spokes in such a form because the slanted spoke becomes longer than a radially extending spoke, and thereby mechanical strength of the spoke is sacrificed. Further, it is not desirable to form the slanted spokes in a die-casting process because a molten metal flow is not smooth compared with the radially extending spokes.